1. Field of the Invention
The present invention relates to a printing apparatus that has a plurality of print engines which each generate one of i printed images of a job and properly stack the printed images.
2. Description of Related Art
Currently there are printing machines that electronically image and print on sheets using a single print engine to produce printed output at a rate n images per minute. To obtain increased speed the print engine must be driven at an increased speed. The increased speed introduces various design problems including sensitivity of the photosensitive member, the developing process, cleaning, transferring and other processes limited by the mechanical construction. Ultimately there is a limit to increasing the speed of print engines to produce higher speed output.
U.S. Pat. No. 4,125,874 issued to Higashide et al. describes a technique for controlling the printing of data supplied by a processing unit at a plurality of remote printers. The Higashide system uses an addressing scheme wherein the processing unit can send out a plurality of addresses each designating a selected printer to print the data, then send out the data in only one transmission for printing by the selected printers.
U.S. Pat. No. 4,587,532 issued to Asano, describes a recording apparatus having a plurality of recording units. If more than one copy is requested, the copy job is divided among the available recording units to provide parallel printing.
U.S. Pat. No. 4,774,524 issued to Warbus et al., discloses a drive arrangement for a plurality of print engines in tandem where the recording medium is passed through two or more printing devices to achieve two-sided printing or multicolor printing. The invention describes synchronization methods to control the medium as it passes from device to device.
U.S. Pat. No. 5,179,637 issued to Nardozzi, discloses a system for distributing print jobs from a data source among a set of print engines and associated image processors of the type having an input data bus. A scheduler coupled to the bus receives data from a print image data source and transfers it to an image processor not currently processing received data. The image processor develops a set of print engine data files from the received data along with data indicating the number of copies of each image or page to be printed and the medium on which it is to be printed. The image processor then identifies print engines that are free and capable of printing images or pages of the data files and distributes the data via the input data bus to the free print engines through their respective image processors.
U.S. Pat. No. 5,220,674 issued to Morgan et al., discloses an improved print server that load balances the print jobs so certain printers are not idle while others have unserviced print requests in a queue. The server includes a resource manager for receiving resource requests from printers and in response forwards the resources to the printers.
U.S. Patent No. 5,287,194 issued to Lobiondo, discloses a print scheduling routine that provides optimum scheduling of jobs on a network. The routine uses the total complex of local and remote printers to allocate and complete printer jobs based on user criteria relating to job requirements including requested completion time. If a single printer cannot satisfy the criteria, the job is allocated to a plurality of printers each printing a portion of the complete job.
U.S. Pat. No. 5,299,296 issued to Padalino et al., describes an improved method of scheduling and switching between jobs in a multifunction machine such as a combination printer/copier/fax machine.